Removal of chlortetracycline from water by immobilized Bacillus subtilis on honeysuckle residue–derived biochar

Biochar-immobilized microorganism technology is an effective way to remove antibiotic contamination in aqueous solutions. In this study, the effect and mechanism of immobilization of Bacillus subtilis by honeysuckle residue–derived biochar for the removal of chlortetracycline (CTC) were investigated using corn straw biochar as a comparison. The biochar’s structural characteristics and properties were determined using scanning electron microscopy, X-ray diffractometer, Fourier-transform infrared spectrometer, specific surface area, and pore size analyzer. It was found that honeysuckle residue–derived biochar had a well-developed pore structure, which provided adequate living space for microorganisms. The removal rate of CTC (50 mg/L) by honeysuckle residue biochar-microbial complex (HBCM) was 15.31% higher than that of corn straw biochar-microbial complex, indicating that HBCM was an excellent carrier. The mechanism of CTC removal by HBCM was a synergistic effect of biochar adsorption and microbial degradation. The removal process of HBCM material was carried out for 3 days at an optimum substrate concentration of 50 mg/L, an ambient temperature of 35 °C, a solution pH of 7, and the addition of 5 g/L complexes, achieving a removal rate of 78.35%. In addition, the complex possessed high storage stability and could be reused three times continuously and efficiently. This study provides a method for preparing an efficient biochar-microbial complex using Chinese medicine residue waste substrate, which provides a new idea for removing CTC from water.